Prior to the present invention modulation of a large aperture radiation source was achieved by placing in front of such source a rotating and stationary wheel of alternating opaque and transparent radial segments. In this arrangement all wavelengths are modulated with the same temporal waveform. For certain applications it is necessary to modulate a single radiation source to provide simultaneously distinct outputs in different spectral regions and at different pulse repetition frequencies.
Accordingly, it is an object of this invention to provide a new and novel mechanical modulator.
It is another object of this invention to provide a mechanical modulator to obtain simultaneously but independently radiation in distinct spectral regions at different pulse repetition frequencies.
Briefly, in one embodiment a mechanical modulator which provides simultaneously two distinct signals in two spectral regions at different pulse repetition frequencies includes three wheels: a first filter wheel rotating at a first velocity having first and second alternating radial segments, said first segments being transparent at both spectral regions and said second segments being transparent at the shorter of the two spectral regions and opaque at the longer; a second filter wheel rotating at a second velocity having first and second alternating radial segments, said first segments being transparent at both spectral regions and said second segments being transparent at the longer of the two spectral regions and opaque at the shorter; and a third wheel which is stationary, also having first and second alternating radial segments, said first segments being transparent at both spectral regions and said second segments being opaque at both spectral regions. This third wheel is arranged intermediate the first and second filter wheels. When the rotating filter wheels are spun past the stationary wheel modulation is obtained in that spectral region where the segments are opaque; the first filter wheel modulates the longer wavelengths and vice versa.
If desired, additional modulating wheels or other types of modulators may be used to superimpose modulation on the outputs from the aforementioned modulator.